How long can blood samples be left at room temperature before they are no longer viable for testing?

Blood Sample Storage Time Limits at Room Temperature

Blood samples should be processed within 2 hours of collection when kept at room temperature to maintain optimal specimen integrity and testing accuracy. 1

General Guidelines for Blood Sample Storage

Serum Samples

• Place blood collection tubes upright at room temperature for 30-60 minutes to allow clot formation 1
• If not centrifuged immediately after clotting, refrigerate (4°C) for no longer than 2 hours 1
• Total processing time from collection to freezer should not exceed 2 hours 1

Plasma Samples

• After collection, keep blood at room temperature and process as soon as possible, preferably within 1 hour 1
• Blood samples should be centrifuged within 2 hours of collection to minimize degradation of biomarkers 1
• Based on stability of coagulation factors, plasma should be used within 4 hours of preparation 1

Storage Temperature Considerations

Room Temperature Storage

• Most analytes begin showing significant changes after 2 hours at room temperature 2
• Specific analytes affected by prolonged room temperature storage:
  • Lactate dehydrogenase (LD): increases from 12 hours 2
  • Potassium (K): decreases from 6-12 hours, then increases after 24 hours 2
  • Glucose: decreases from 3 hours 2

Refrigerated Storage (4°C)

• If processing must be delayed, refrigeration is preferred over room temperature for most specimens 1
• In unavoidable circumstances, blood samples may be refrigerated for up to 24 hours, but this is not optimal 1
• Avoid direct contact of blood tubes with ice to minimize cell lysis 1

Sample Type-Specific Considerations

Complete Blood Count (CBC)

• Should be analyzed within 2 hours at room temperature
• EDTA tubes must be gently inverted 8-10 times immediately after collection 1

Coagulation Studies

• Process within 2 hours of collection 1
• For platelet-rich plasma, use within 2 hours of preparation 1

Chemistry Panels

• Process within 2 hours to avoid falsely elevated potassium and phosphorus levels 2
• Glucose values decrease significantly after 3 hours at room temperature 2

Common Pitfalls to Avoid

1. Prolonged exposure to heat: Extreme temperatures can accelerate enzyme degradation and affect test results
2. Delayed separation of cells from plasma/serum: Leads to metabolism by cells, changing analyte concentrations
3. Multiple freeze-thaw cycles: Can significantly reduce enzyme activity
4. Improper tube mixing: Inadequate mixing can lead to incomplete additive distribution
5. Ignoring specific test requirements: Some specialized tests have unique handling requirements

Special Circumstances

For certain specialized tests or research protocols, longer room temperature storage may be acceptable:

• Blood bank specimens: Up to 2 hours for reissuing blood units 3
• Whole blood for platelet production: Can be held overnight (24-26 hours) at room temperature 4, 5

Remember that these exceptions are for specific purposes and do not apply to routine clinical laboratory testing, where the 2-hour rule should be followed to ensure accurate results that impact patient care decisions.